Although often considered to be a disease of adults, complications of ADPKD begin in childhood. While the hallmark of ADPKD is the development and continued growth of multiple renal cysts that result in ultimate loss of kidney function, the leading cause of death among affected patients is cardiovascular in nature. Vascular dysfunction (endothelial dysfunction and large elastic artery stiffness) is evident very early in te course of the disease and appears to involve increased oxidative stress and inflammation. Treatment options to prevent CVD in adults with ADPKD are limited, thus childhood may represent a key therapeutic window. Curcumin is a safe, naturally occurring polyphenol found in the Indian spice turmeric that has a unique ability to activate transcription of key antioxidants, suppress inflammation, and reduce proliferation. Aim 1 will assess the efficacy of curcumin (25 mg/kg/day) for improving vascular function in children and young adults (6-22 years of age) with ADPKD, using a 1 year randomized, placebo-controlled, double-blind trial. Aim 2 will determine (in a sub-group of patients 18-22 years of age), if improvements are associated with reduced oxidative stress and inflammation, utilizing state of the art mass spectrometry methods. A third exploratory aim will assess changes in total kidney volume using MRI scans. This study has the potential to establish a novel, safe, and easy to deliver therapy for the treatment of arterial dysfunction, and possibly renal cystic disease, in an understudied population of children and young adults with ADPKD.